Sensitive ${\rm NH}_{3}{\rm OH}$ and HCl Gas Sensors Using Self-Aligned and Self-Welded Multiwalled Carbon Nanotubes

Abstract

We present the design and fabrication of sensitive and responsive NH 3 OH and HCl sensors based on multiwalled carbon nanotubes (MWCNT). The sensors consisted of self-aligned and self-welded MWCNT bridges grown between 18 m-high silicon posts with 2-6 m gaps using metal-catalyzed chemical vapor deposition technique (CVD). The 5-10 MWCNTs spanning the gap showed excellent Ohmic electrical contacts and mechanical bonding strengths in excess of 0.1 N/CNT. The conductivity of the MWCNTs changes as oxidizing and reducing gases are physically adsorbed on their large surface-to-volume ratio structures. Since carbon atoms in CNTs do not have any dangling bonds, the interaction between CNTs and gas molecules does not lead to chemical reactions and the process is reversible.Provided that the starting MWCNTs have high resistivity, they have nearly exponential sensitivity in detecting gases and owing to their very small volume and reversible interaction with gases, they can have a very fast response time.In our experiment, upon exposure to ammonia and hydrochloric gases at room temperature, the electrical conductivity of the self-welded carbon nanotube bridges exhibited a dramatic change. The growth process, test results, and the gas sensitivities will be discussed.Index Terms-Bottom-up technique, multiwalled carbon nanotubes (MWCNTs).

A Review of Carbon Nanotubes‐Based Gas Sensors

“…Figure 4 shows the structure of the sensor and the laterally aligned CNTs connecting the electrodes. Tabib-Azar and Xie [28] also successfully prepared selfaligned and self-welded MWNTs between prepatterned electrodes by low pressure CVD (LPCVD) for NH 3 OH and HCI sensing. Ding et al [29] achieved the growth of aligned CNTs in an anodic aluminum oxide (AAO) template for hydrogen sensor.…”

Efficient encapsulation of conducting polyaniline chains inside carbon nanotubes: a new strategy to prepare endohedral CNT materials

“…This is similar to the observation from Tabib-Azar in view of the donor-compensating effect. 34 Compared with the pure CNT membrane and the PANi coated CNT membrane, the PANi@CNT membrane shows a much higher resistance response. The resistance change (R/R 0 ) of the PANi@CNT is found to be 5 times and 9 times larger than the PANi coated CNT sample and the pure CNT lm respectively when facing 5000 ppm NH 3 .…”

Lateral MoS2Heterostructure for Sensing Small Gas Molecules

“…In view of those drawbacks and the need for a higher sensitivity, new materials have been investigated. These include low dimensional materials such as graphene sheets, − graphene nanotubes, − and semiconducting nanowires, − but also TMDC monolayers, − and other 2D heterostructures . In 2D structures, the high surface-to-volume ratio is expected to promote specific binding or adsorption on their surface and enhance their potential as an essential component in sensors .…”